In general, the first circuit based on the charge transfer principle to enable a voltage/voltage converter to be made on an integrated circuit was proposed by Mr. J. F. Dickson in an article entitled “On-chip high-voltage generation in NMOS integrated circuits using an improved voltage multiplier technique” which was published in June 1976 in the journal “IEEE J. Solid-State Circuits, Vol. 11, pp. 374-376”. That circuit referred to below as the “Dickson” circuit presents a structure that is not symmetrical and that is constituted by capacitors and NMOS transistors connected as diodes. The function of the capacitors is to store electric charge, whereas that of the transistors is to act as switches to control charging of the capacitors and to transfer charge between capacitors. Since the publication of that article, most voltage/voltage converters of non-symmetrical structure have been implemented on the basis of the above-mentioned Dickson circuit, but they suffer in particular from the drawback of leading to a loss of voltage due to imperfections in the NMOS transistor switches.
Elsewhere, a “Clock Booster” circuit implemented in CMOS technology is described in an article entitled “An experimental 1.5 V 64 Mb DRAM” published in April 1991 in Volume 26, pp. 465-472 of the above-mentioned journal, with such a circuit of geometrical structure enabling a direct current (DC) component to be added to a clock signal. That circuit is referred to below as the clock booster circuit.
In general, integrated CMOS voltage/voltage converters are used in two main fields in particular, specifically: EEPROMs, also referred to as FLASHROMs, and low-voltage integrated circuits in order to feed certain portions of such circuits with higher voltages EEPPROMs are presently used in numerous consumer applications such as, for example: digital cameras, MP3 digital audio players, and pocket computers, and demand for memories of this type has increased considerably over the last few years. Low-voltage integrated circuits are also in full expansion and are used in particular in consumer products such as cell phones and the above-mentioned portable appliances.
Specifically, the technical problem to be solved is for the output voltage from the converter to be increased as much as possible for a given number of stages. With a portable appliance powered at 3 volts (V) from a battery, for example, it is necessary to obtain a programming voltage of 9 V in order to be able to store information in a memory of the FLASHROM type.
In theory, if a voltage/voltage converter were perfect, then a two-stage voltage tripler would suffice to produce such a 9-V programming voltage. Unfortunately, experience shows that a voltage/voltage converter of non-symmetrical structure implemented on the basis of the Dickson circuit needs to be a three-stage voltage quadrupler in order to produce the above-specified programming voltage.
In the prior art, document WO 02/43232 describes a voltage/voltage converter in accordance with the pre-characterizing portion of claim 1.